From iA wiki
Acronym: Emerging Network To Reduce Orwellian Potency Yield
Support forum: http://f27.parsimony.net/forum66166/
A P2P application based on the same ideas as Freenet, but written in C instead of Java. It is very fast (compared to Freenet), but has a smaller user base. From the user's perspective it is similar to Freenet, including the same concepts of KSK, SSK, and CHK keys, and freesite browsing through a web browser interface.
To maintain compatibility, ENTROPY implements a FCP port that is backwards compatible with Freenet applications like Frost, FIW, and FMB. The only thing that one needs to change to use a Freenet application on ENTROPY is the port number (ENTROPY uses a default FCP port of 8482 instead of 8481). There also have been some extensions made to the FCP protocol to add a few small features like the ability to limit the size of a key to be retrieved, and to automatically configure the maximum HTL. Currently, only Samizdat uses these features.
Despite its similarities to Freenet, there are also a number of differences. The most apparent to the end user is the inclusion of a message board in the web proxy. This allows users to read and write messages without having to install special software like Frost. However, if you do want to use an external program, the message board is compatible with Frost and Samizdat.
Another difference is that ENTROPY handles large files automatically. On Freenet, each client program has to include code to handle splitfiles. ENTROPY takes a different approach, by putting splitfile handling in the ENTROPY program itself. This means that FCP client authors can write their programs without having to worry about splitting and reassembling large files. Large files can be inserted in exactly the same way as small files, without any special programming. Of course, if the client program wants to handle splitfiles itself, it can, but it is unnecessary except for compatiblity with Freenet.
From a cryptographical standpoint, ENTROPY is also different from Freenet. It uses a McEliece public key system, and has several different stream ciphers to choose from (five at the time of this writing, plus one unencrypted stream mode).